“MSL is very, very complicated,” says Rob Manning Curiosity chief engineer. “It is almost hard to imagine how complex it is,” he says in this video, shot to convey the extraordinary NASA and contractor technology and testing that has gone into the MSL program. JPL video.
Diverse lunar and planetary exploration in 2011 by NASA should help dispel the widespread notion that the U. S. civilian space program is dead following phase out of the space shuttle. In fact the Mars Science Laboratory (MSL) rover Curiosity launched Nov. 26 is propelling NASA into the future just months after the final shuttle mission recalled U. S. space glories of the past.
NASA has scored big throughout the solar system this year. Key highlights include:
—Messenger in 2011 became the first spacecraft to orbit Mercury revealing previously unknown details of the planet and the solar system’s formation. Messenger’s discoveries are so numerous that they were part of 63 presentations spanning 13 technical sessions at the American Geophysical Union’s annual meeting in San Francisco last week.
—Dawn which arrived at the giant asteroid Vesta this year, has just confirmed that the body is a genuine protoplanet with differentiated features more like Mercury, Venus, Earth and Mars than a homogeneous asteroid.
—New Horizons is more than half way to a 2015 flyby of Pluto. During 2011 it moved closer to Pluto than any previous spacecraft.
—Lunar Reconnaissance Orbiter this year completed the first high resolution topographic map of the moon and returned extremely high resolution images of the Apollo 12, 14 and 17 landing sites.
—Twin ARTEMIS spacecraft achieved lunar orbit early in 2011 to study the Sun’s interaction with the moon.
—Twin GRAIL spacecraft are to enter lunar orbit by Jan. 1 for lunar gravity studies, marking 5 U. S. lunar orbiters that will be operational above the moon by New Years Day. They are part of the most intensive studies of the Moon since the Apollo program.
—Juno with advanced technologies for outer planet exploration launched this year on a five year transit to orbit Jupiter for the first detailed studies of the spectacular Jovian atmosphere.
—Cassini has this year continued to make discoveries about Saturn and its moons including finding water vapor in the geysers of Enceladus and seasonal methane rains on Titan that swell and sculpture its rivers and lakes just like water does on Earth.
—The Mars rover Opportunity, nearing the 8th anniversary of its landing in Jan. 2012, has just won NASA’s top software award for 2011 for implementing autonomous imaging capability.
During 2011 it completed a 3 yr. 13 mi. drive to large Endeavour crater where it has found clay-like deposits requiring water to form. And in a major discovery Oppy has just found bright veins of the mineral gypsum, deposited by water.
“This tells a slam-dunk story that water flowed through underground fractures in the surrounding rock,” said Steve Squyres of Cornell University, principal investigator for Opportunity. “It’s not uncommon on Earth, but on Mars, it’s the kind of thing that makes geologists jump out of their chairs,.” he said at the AGU conference .
—Mars Reconnaissance Orbiter (MRO) during 2011 confirmed that Mars currently has flowing water, detected emerging during warm periods out the sides of Martian crater rims. MRO is still intensively imaging the Gale crater region to support MSL landing and roving operations.
MSL in flight, filmed from Brisbane, Australia, appears as a tiny dot moving from top left to lower right against the stars along with the white gas from the venting of residual propellants from its Centaur upper stage. The sighting occurred about 20 min. after the 22,500 mph escape burn from Earth performed over the Indian Ocean. The brilliant streak at start of video is the Delta II second stage for the Deep Space I launch 13 years ago. Images by Duncan Waldron.
“MSL is an amazing technological achievement,” said Colleen Hartman NASA assistant assoc. administrator for the Science Mission Directorate.
While the skycrane landing system draws the greatest attention, it is the coupling of active guidance with aerodynamics to fly–rather than fall– in the Martian atmosphere that will be the key to MSL’s ability to make a precise landing in early August.
It has far more computing capability than the MER Mars Exploration Rovers Spirit and Opportunity that each had only a single, much less capable computer. Curiosity has two BAE RAD 750 computers with a PowerPC 750 architecture that operates at up to 200 MHz speed 10 times faster than the MER rover’s single processor. Each of Curiosity’s 2 computers also has 2 gigabytes of flash memory, 8 times more than the MERs.
MSL’s parachute has a direct heritage to past Mars missions, but its thrusters and landing engines are the oldest component designs on the spacecraft. Its eight Mars landing engines go back to Viking in 1976 and more than 320 engines from MSL’s two main thruster groups have already flown in space going back 20-30 years over the course of dozens of space missions. But everything else on MSL involved in landing is cutting edge new.
On landing day Aug. 5 Mars will be 154 million mi. from Earth and 109 years beyond when the Wright Brothers made fundamental breakthroughs in aeronautics including the merger of precise lift calculations, with attitude control.
Those discoveries by the Wright Brothers will finally bridge time and technology, translating into to flight in the atmosphere of Mars with the MSL heatshield acting as a “lifting” airfoil to begin the 400 sec. descent from space.
The guided reentry, landing radar and skycrane have undergone extraordinary computer and physical hardware tests including 4 million simulated Mars landings this year alone in powerful computers at the NASA Langley Research Center, Hampton, Va.
Millions more tests will be run right up until landing day, said David Way, the Langley engineer leading the simulations.
This precision entry and landing, coupled with the skycrane delivery system will give NASA a new workhorse Mars landing system for use by future landers and rovers that, like Curiosity, are 2,000 lb. or heavier. Future manned Mars operations may require precise landings of 40-100 ton payloads.
Five times heavier than Spirit or Opportunity, Manning said the MSL rover is “by far” the most ambitious spacecraft ever developed by the Jet Propulsion Laboratory, Pasadena, Calif.
The supersonic parachute for the MSL was tested at the NASA Ames Research Center in the world’s largest wind tunnel. The parachute has 80 suspension lines over 165 ft. long, and is about 51 ft. in diameter. The parachute can generate up to 65,000 pounds of drag force in the Martian atmosphere. In Earth’s atmosphere the tunnel can generate the same relatively low speed air flow velocity that the parachute will experience when it opens at 1,000 mph above Mars in the planet’s thin atmosphere. JPL/Ames video
As many as 5,000 people in NASA and companies around the world have participated in its development.
“It is difficult to overstate what a major step forward this is beyond the earlier Mars Exploration Rovers” said Pete Theisinger MSL project manager at JPL.
Curiosity’s computer using atmospheric entry algorithms from the Apollo program will steer by ejecting heavy tungsten ballast at two different times during atmospheric entry. This will alter the vehicle’s center of gravity, enabling the MSL aeroshell to fly at differing angles of attack.
It will also perform left and right hypersonic bank maneuvers at up to about 70 deg. of bank to change its lift vector to adjust it’s range and descent rate to precisely navigate to its touchdown area. This will be exactly like the space shuttle used similar bank maneuvers during reentry.
MSL is also more than twice the physical size of the Mars Exploration Rovers (MERs) Spirit and Opportunity rovers that landed in 2004, and Curiosity carries 150% more science payload mass.
For science, Curiosity is outfitted with 10 instruments and a maze of Martian sample transport paths, mini laboratories from the U. S., ESA and the national space agencies of Canada, Spain and Russia. It will roam a water-rich Gale crater region to search for the carbon based building blocks of life.
Key differences between Spirit and Opportunity and the new MSL rover Curiosity are:
—Wheels and speed: Curiosity will use six wheels each 50 cm in diameter. This compares with the 20 cm wheels for Spirit and Opportunity. The larger wheels will give Curiosity a 20% increase in max speed to 6 cm/sec. compared with Spirit and Opportunity. It larger wheels will enable curiosity to climb over larger rocks, up to 29 in. high.
—Mission duration: The formal MSL mission specification is for at least 2 Earth years of lifetime while driving up to 20 mi. Opportunity is entering its 8th year of operations and has passed 15 miles on its odometer.
—Science mass: MSL will carry 187 lb. of science instruments and sample acquisition tools compared with about 11 lb. for Spirit and Opportunity.
—Size comparison: Curiosity is 8.8 ft. wide, 7.2 ft. tall and 9 ft. long compared with the two MER rovers that each were 7.5 ft. wide, 4.9 ft. high and 5.2 ft. long.
—Radar: Another key to accuracy and a safe landing will be a new radar configuration never flown to Mars before. “The radar has taken substantially more time to develop than desired, but it is a superb radar,” says Pete Thesinger, MSL project manager at JPL.
“We needed good velocity and altimetry data relative to surface of Mars. When slowing from nearly 4 mi. per sec. It is tough to get the velocity data correct down to under a meter per sec.—and that is what we need to land this thing,” said Steltzner.
“We feel great about the radar,” Adam D. Steltzner JPL entry, descent, and landing manager for MSL said. “One reason we decided to build our own radar is that we struggled in the past with Phoenix, MER and Pathfinder radars when we tried to modify existing weapons system radars,” he said.
In tests at NASA Dryden the six radar transmitters and pickups were mounted on helicopter on same shaped mount as on the skycrane. The helicopter then used the radar data to descend at the same rate the skycrane will fly till rover descends on lines, duplicated by the Dryden tests. It then slowed its descent further as rover gently touched down. Two descents are shown. JPL/Dryden video.
During its 9 month 354 million mi. curving trajectory from Cape Canaveral to Mars the aeroshell with skycrane and rover inside are flying attached to a large disk shaped cruise stage with solar cells on top. During cruise the aeroshell will have a symmetrical mass.
The 22,500 mph planetary trajectory injection accuracy achieved by the Atlas V Centaur’s upper stage guidance system has been so precise, that an initial planned trajectory correction maneuver (TCM) set for two weeks after launch was canceled. The first TCM will now be about March 24 followed by a second in early June that will actually target MSL onto the landing site. Up to three more TCM’s are possible after that including one just 9 hr. before entry if desired.
There will also be at least two software uploads from JPL to MSL during cruise as all of its landing systems and science instruments are powered on for tests. The JPL control and science teams are also beginning major Operational Readiness Test (ORT) simulations. Those will accelerate in the spring in preparation for landing Aug. 5 at about 10 p.m. PDT and 3 p.m. local time on Mars.
The final version of Curiosity’s landing software will be unlinked in May, followed in June by the transmission of software for the rover’s Martian surface operations, said Theisinger.
“The rover already has software to do individual tasks,” he said. “What we’re adding is greater efficiency so we can tell it to do something and then it can execute a whole block of activities in one go,” Theisinger said.
“During entry we will fly a symmetrical aeroshell body with asymmetric mass,” Steltzner said.
Separation of the cruise stage will occur about 10 min. before the start of the entry. Just after cruise stage separation and before entry 330 lb. of ballast will be ejected.
“That will make us fly at a canted angle that will enable the heat shield to develop lift. Steering and lift control will be achieved by the rover computers calculating when to fire attitude control jets to roll or bank the vehicle.
For the first time in any Mars landing, the attitude and velocity of the vehicle will be used continuously in a closed loop data stream for real time maneuvering commands to landing within the small 12 mi. wide by 15 mi. long landing ellipse.
The untested skycrane still must work perfectly after the high and fast portion of the reentry brings MSL into the Gale crater area. Here is how that will happen:
—Second ballast ejection: Just before parachute deploy another 330 lb. of tungsten ballast will be separated, this time to relocate the center of gravity back to the middle of the vehicle to provide a balanced condition for the rest of landing events.
—Supersonic Parachute deploy: Velocity measurements will deploy the single Pioneer Aerospace 52.5 ft. dia. parachute when the vehicle has slowed to 1,000 mph at about 6 mi. altitude. On MSL the chute will be lowering a mass of 3,400 lb. including the aeroshell, skycrane and rover.
—Heat shield separation: After the parachute opens the heat shield will be jettisoned. This opens the bottom of the aeroshell and cues activation of the landing radar with transmit and receive heads on a bat shaped tray extending off the side of the rover.
—Real time imaging: The Mars Decent Imager attached near the lower side of Curiosity will begin taking a continuous stream of high resolution images at up to 4 /sec. Developed by Malin Space Science Systems, the imager will look down on the terrain, showing it grow closer and closer during the landing.
—Backshell and parachute separation: Descending through 6,000 ft. at 180 mph the vehicle will separate its backshell and parachute revealing the Mars skycrane and sports car sized rover.
—Powered descent: Things begin to happen fast at backshell/parachute separation. The sky crane has eight 675 lb. thrust Mars Landing Engines (MLEs). Now, 154 million mi. from Earth, the vehicle is free for its historic landing on Mars—or a heartbreaking crash.
The first thing the skycrane and Curiosity do is nothing. The vehicle is programmed to freefall for 1 sec. to be well clear of the 100 ft. long parachute canopy, risers and backshell.
Paired on each corner of the skycrane, all 8 MLEs are ignited as the skycrane and rover streak through 6,000 ft. at 180 mph. Engine ignition will dramatically slow the descent and gain attitude control for the fast approaching Martian touchdown.
Entry, descent and landing (EDL) combines many new Mars landing technologies. JPL video
The first thing the vehicle does is maneuver laterally 1,000 ft. To prevent the disaster of having the backshell and parachute collide in midair or accidentally drop onto what had been a safely landed rover.
The sky crane still holding Curiosity tight will begin to descend at 32 meters per sec. –71 mph—for about 3 sec. It will then slow to a sedate 7 mph descent rate.
After the lateral maneuver the sky crane’s thrusters will null out motions in all axis that may be left over from the separation of the parachute. The radar will temporarily stop looking for the ground and shift to velocity measurements to establish this rate.
During this period, the rover will be flying in one of three “terrain accordions” where there will be ample room for the computers to command major adjustments in altitude and velocity.
When the engines have slowed the descent to 1.7 mph, four of the 8 MLE’s are throttled to only 1% as MSL holds that slow velocity until touchdown. The other four are throttled as needed in the 30-50% power range.
As the descent continues to 66 ft. altitude the rover is released by the skycrane and begins to be lowered on its triple line 60 ft. bridle (BUD) just 12 sec. from touchdown. The rover will unfold its six wheeled rocker bogie mobility system midway in the descent.
The scene will be of endless red terrain, with a looming mountain in the middle of giant Gale crater below, as the two vehicles now fly for several seconds as two distinctly separate vehicles connected by the BUD cords.
The rover will drop more rapidly on the bridal than the skycrane is descending. As it reaches the surface the rover computer will sense the skycrane trying to accelerate upward, since it just lost 1 ton of payload mass. This will cue Curiosity to open latches, severing connections holding the rover onto the bridal. It will also cue the skycrane to begin its flyaway maneuver to fly out of the area and crash about one half mile away.
“We love to smartly say that we do not look for the touchdown event, but rather perceive the post landing state of the vehicle” Steltzner said. It will be about 3 p.m. at the Gale crater site. The touchdown will occur on Sol zero of the flight.
Curiosity will take some initial images with its front and back hazard cameras but will not raise its mast with the best imaging systems till Sol 1 the following day. It will slowly move into science instrument checkout, and will likely process initial soil and perhaps rock samples directly from the spot where it lands. Initial roving may not occur until Sols 3 or 4.
One of the internal labs that will be tested is the Goddard Sample Analysis At Mars (SAMS) that has a 100,000 rpm pump with components that must turn at 1,666 times per sec.
Initial arm deployments will also be done. “In terms of mass and strength this 7.5 ft. MSL arm is much beefier and stronger than the 3 ft. MER arm, says Matt Robinson, lead engineer for robotic arm systems. “Just the turret on the MSL arm weighs more than the whole arm electronics and science on the smaller MER rovers, Robinson said.
“We have a whole different style of motions with the MSL arm, because we use a lot more “gravity relevant” motions to move samples where we want them to fall inside the mechanisms,” says Chris Leger, robotic arm flight software developer and the surface software development lead for the MSL flight.
“When we do sample processing you will see the turret spin around to do different sample orientations, while other actuators are creating vibrations.
A lot of arm trajectory calculations will be specific to the turret to get samples in test chambers and to move them through the internal sample paths.
The arm uses a percussion device to break rock into power that can be moved to the rover’s mini labs. “There are at least 50-100 different arm motions to get the samples out of the drill and over to the instruments,” Leger said.
“It is a complicated series of operations that we do,” he said. “We are trying to make the software do more of that on board than we could do with MER rovers.
On MSL (unlike the MERs) the team will not have to write a sequence of hundreds and hundreds of lines of software for daily operations. “With MSL we will have those kinds of sequences developed here at JPL then already on board the rover,” Leger said.
John Grotzinger the MSL project scientist explains most likely roving routes for Curiosity in Gale crater. JPL video